Fuse



P. L. SPENCER FUSE Filed Jan.2l, 1942 Nov. 23, 1943.

FIG 2;

P IIiiVESNTOR. B 6am TTY prevented. The envelope Patented Nov. 23, 1943 FUSE Percy L Spencer, West Newton, aslignor to Raytheon Production Corporation, Newton, Mass, a corporation of Delaware Application January 21, 1942, Serial No. 427,812 3 Claims. l'Cl. 200-125) This invention relates to improvements inelectricalfuses.

An object of this invention is the provisionof a fuse for precise operation on small currents.

Another object of this invention is'the provision of a fuse which will of itself tendto limit the current to a predetermined value.

A further object of this invention is the provision of a multiple fuse device which is so constructed that when one fuse element has been destroyed by an overload of current others are available without requiring the substitution of another fuse device.

I A further object of this invention is the provision .of a fuse adapted to be arranged in a radio tube socket. 1

Still another object of this invention is the provision of a fuse device which is simple to com struct and reliable in operation.

A further object ofthis invention is the provision of afuse device which can be constructed at relatively low cost.

Other and further objects and advantages of this invention, and the hereinbefore mentioned objects, will become clear from-the following description'of an exempliflcation thereof, reference being had to the drawing, in which Fig. 1 is a top plan view of a fuse device embodying my invention; I

Fig. 2 is a perspective view, partly broken away,

of said fuse device and includes a plan view ofa socket; and

Fig. 3 is a schematic diagram of a circuit within which said fuse device is adapted to be arranged.

The fuse-device 1 consists of a glass envelope [having a bottom wall consisting of a stem or -.base 3. A plurality of lead-in rods 4 are sealed through said stem 3. These lead-in rods are made of some metal which readily seals to the glass of said stem, and may conveniently be made of chrome iron. The lead-in rods 4 are disposed in a circle concentric with the center of the stem 3. These lead-in rods are also rigid so that in the completed form of the tube they serve as the external contact pins adapted to be inserted into a cooperating tube socket 5. i the glassy envelope 2 is surrounded by a guard shell 6 held in place on the envelope by means of a ring of cement I. The guard shell 6 is provided with sufficiently large openings around each of the lead-in rods 4 so that electrical contact between the shell 6 and the rods 4 is effectively 2 is provided at the central portion of the ,base3 with an exhaust opening communicating with an exhaust tube 8.

The bottom of 1 in socket 5.

The envelopeis exhausted through the exhaust adapted to fit into openings l I within said socket and make contact with the contacts l2'therein.

The socket 5 is a radio tube socket. By the term radio tube socket I mean herein and in the claims the standard radio receiving tube type of socket now in common use. The socket herein illustrated is known as the octal" type and has eight openings ll adapted to receive eight contact pins l3 which are the protruding portions of lead-in rods 4. I

The fusible elements are adapted to be secured to the upper portions i4 of lead-in rods 4. For this purpose I prefer to use a wire having a relatively high positive temperature coefiicient of resistivity. A wire Ii'made of iron or nickel has been found satisfactory. This wire is wound around the eight upper portions l4 of the lead-in rods 4, leaving a space between two of them l6 and i1, so as to prevent a complete turn from being made. The wire i5 may be secured to the upper portions I 4 of the lead-in rods 4 by welding said wire thereto. Each portion of the wire l5 between the upper portions 14 of the lead-in rods 4 serves as a separate fuse except between upper portions l6 and H between which the wire does not run. It will be noted therefore that each of the upper portions I4, except l6 and 11, serves as a I common conductor for two fuse elements.

rent passing therethrough. Furthermore the increased resistance generates more heat, raising the temperature of the wire, to thereby produce cumulative action which causes rapid burn-out of the fuse wire.

Two of the contacts it of socket 5 are arranged in a circuit to be protected from current overloading. A source of E. M. F. [8, and a load l9 are arranged in series with each other and connecte to said contacts. When the fuse device I is arranged in the socket 5 using the tubular member 9 as a centering guide and inserting said tubular member 9 within the opening ID in said socket, the contact pins l3 touch the contacts l2.

In the ordinary radio tube socket, such as socket 5, a keyway is provided for receiving the key customarily provided on the tubular positioning member projecting from the base of the radio receiving tube. Since no key is provided on the tubular member 9 the fuse device I can be placed in any position so that any two adjacent contact pins l3 may be arranged to touch the contacts I! which are connected in the circult to be protected. It will be readily seen that when one of the fuse elements burns out said fuse device may be raised slightly out of the socket so that the contact pins I! are cleared of the top of said socket and the fuse device may then be rotated to bring contact pins connected with an unfused fuse element into position for insertion in those openings II which have their contacts l2 connected to the circuit to be protected. Since the lead-in rods 4 are spaced an equal distance from each other and since the wire is is of uniform cross section it will be apparent that the fuse element between any two of the lead-in rods will be equal to that between any two others. It will, of course. be understood that contact pins l3 connected with upper portions 16 and I1 are not to be arranged in contact with the contacts I! which are connected to the circuit to be protected since there is no fuse wire between these two upper portions.

In actual practice it has been found that fuse devices such as hereinbefore described are simpie to construct and require no special skill. Such fuses although made by relatively unskilled hands have been found to be reliable in operation and extremely uniform. For example, a number of fuse devices made in the manner hereinbefore described included a fusible wire having a diameter of .00046 of an inch and was three inches in length.- This wire was wound round the lead-in rods 4 and welded to said rods to form seven separate fuse elements. The wire used was made of nickel with approximately one per cent. of other metals, including carbon. This was a milliampere fuse. Tests made with a number of fuses of this kind showed a variation of between 1 /2 to 2mil1iamperes plus or minus, at which each of the fuse elements would blow. The variation between the fuse elements in any one fuse device was no greater than the foreg.

While I have described a specific embodiment of my invention it will be understood that the details thereof may be varied without departing from the spirit thereof. For example, instead of a round fuse wire a flat ribbon may be used.

Changes in the shape of the fuse device or in the manner of connecting the fuse elements and/or its conducts will readily suggest themselves. Other changes will be apparent from the foregoing description to anyone versed in the art. Therefore it is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is: r s

1. A multiple fuse unit comprising an insulating base, a plurality of pins secured in said base and forming contact prongs projecting therefrom, said prongs being arranged in a circle with each prong equidistant from its adjacent prongs,

and a unitary fuse member secured and electrically connected at spaced intervals thereof to each of said pins to thereby form a plurality of fuse elements, said unit being adapted to be manually manipulated to bring said contact prongs into contact with cooperating contacts in a socket.

2. A multiple fuse unit for arrangement in a socket, said socket having receiving Openings with contacts therein, comprising a plurality of pins secured in said base and forming contact prongs projecting therefrom, said prongs being arranged in a circle with each prong equidistant from its adjacent prongs, said prongs being adapted to fit into the receiving openings in said socket and make contact with the contacts therein, and a unitary fuse member substantially circumferentially arranged about said pins, said member being secured and electrically connected at spaced intervals thereof to each of said pins to thereby form a plurality of fuse elements.

3. In combination a. multiple fuse unit and a socket in which said unit is adapted to be arranged, said socket having receiving openings with contacts therein and a central positioning opening, said unit comprising an insulating base,

a plurality of contact pins fixed in and extending above and below said base, said pins being arranged in a circle with each pin equidistant from its adjacent pins, said pins being adapted to fit into the receiving openings in said socket and make contact with contacts therein, a circle of fused elements electrically connecting said pins and. a centrally located positioning member projecting from beneath said base and of greater length than the positions of said contact pins extending below said base, said positioning member being adapted to be journaled in the socket positioning opening whereby said unit member may be raised from the socket without completely withdrawing the positioning member and may be rotated so that the contact pins may be inserted in different receiving openings of said socket to thereby place different fuse elements in electric contact with different sets of said contacts.

PERCY L. SPENCER. 

